Employee Benefits - Components of Net Periodic Pension Cost and Other Changes in Plan Assets and Benefit (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Components of Net Periodic Pension Cost
Service cost—benefits earned during the period	$ 0	$ (6)	$ 0	$ 469
Interest cost on projected benefit obligation	1,025	1,099	3,075	3,200
Expected return on plan assets	(1,582)	(1,444)	(4,746)	(4,337)
Amortization of prior service credit	475	29	1,424	(41)
Recognized net actuarial loss	0	638	0	1,708
Net Periodic Pension Expense	$ (82)	$ 316	$ (247)	$ 999